#include <cstdio>
#include <vector>

using namespace std;

vector<bool> b(2000005, false);

int main()
{
    freopen("ciur.in", "r", stdin);
    freopen("ciur.out", "w", stdout);
    int n;
    scanf("%d", &n);
    fclose(stdin);

    for(int i = 4; i <= n; i += 2) b[i] = 1;
    for(int i = 3; i * i <= n; i += 2)
        if(!b[i])
            for(int j = i * i; j <= n; j += 2 * i) b[j] = 1;

    int ct = 0;
    for(int i = 2; i <= n; ++i)
        if(!b[i]) ct++;
    printf("%d", ct);
    fclose(stdout);
    return 0;
}